mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2025-02-01 05:01:59 +01:00
64ad58bc9d
This patch fixes a problem in function 'combineX86ShuffleChain' that causes a chain of shuffles to be wrongly folded away when the combined shuffle mask has only one element. We may end up with a combined shuffle mask of one element as a result of multiple calls to function 'canWidenShuffleElements()'. Function canWidenShuffleElements attempts to simplify a shuffle mask by widening the size of the elements being shuffled. For every pair of shuffle indices, function canWidenShuffleElements checks if indices refer to adjacent elements. If all pairs refer to "adjacent" elements then the shuffle mask is safely widened. As a consequence of widening, we end up with a new shuffle mask which is half the size of the original shuffle mask. The byte shuffle (pshufb) from test pr24562.ll has a mask of all SM_SentinelZero indices. Function canWidenShuffleElements would combine each pair of SM_SentinelZero indices into a single SM_SentinelZero index. So, in a logarithmic number of steps (4 in this case), the pshufb mask is simplified to a mask with only one index which is equal to SM_SentinelZero. Before this patch, function combineX86ShuffleChain wrongly assumed that a mask of size one is always equivalent to an identity mask. So, the entire shuffle chain was just folded away as the combined shuffle mask was treated as a no-op mask. With this patch we know check if the only element of a combined shuffle mask is SM_SentinelZero. In case, we propagate a zero vector. Differential Revision: http://reviews.llvm.org/D13364 llvm-svn: 250027
Low Level Virtual Machine (LLVM) ================================ This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments. LLVM is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. Please see the documentation provided in docs/ for further assistance with LLVM, and in particular docs/GettingStarted.rst for getting started with LLVM and docs/README.txt for an overview of LLVM's documentation setup. If you're writing a package for LLVM, see docs/Packaging.rst for our suggestions.